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Volcanoes/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby A boy, Tim, and a robot, Moby, are exploring mountainous terrain. Tim reads from a typed letter. TIM: Dear Tim and Moby, What makes volcanoes erupt? From, Dylanne. TIM: That's a great question. Volcanoes are openings in the ground that release energy from deep inside the planet. An animation shows the cross section of a volcano as it erupts. Orange lava is shown moving from deep under the surface through several of Earth's layers. MOBY: Beep. TIM: Sure, up here on the surface, the earth seems pretty cool and stable. But miles below our feet, it's a raging inferno. An animation shows layers below the surface where Tim and Moby are standing. TIM: The deeper you go, the hotter it gets. An animation shows the hot area deep inside Earth. TIM: Earth's center, or core, is about as hot as the surface of the sun. All that energy wants to escape, like steam inside a boiling kettle. A circular image shows Earth's core and the layers around it. TIM: It pushes outward, forcing material in the mantle toward the surface. Arrows point from the core to the mantle layer. The mantle is the area between the core and the earth's surface. TIM: Standing in the way is the crust, the planet's rocky outer layer. The crust is labeled. It is Earth's top layer. MOBY: Beep. TIM: Yup, it's paper-thin compared to the other layers, but we're still talking about miles of heavy rock. The rigid crust keeps the mantle material trapped below. But in some places, the mantle forms pockets of magma, molten rock mixed with hot gas. An animation shows layers of the crust. Arrows point to how the crust disperses energy to keep the mantle material trapped. Magma is boiling at the bottom of the layers. TIM: The liquid magma is much less dense than the solid stuff all around it, so it begins rising. As it rises, the dissolved gases form bubbles that rush to escape, shooting the magma up even faster. The animation shows the magma rising up through the layers to the surface. The scene shifts to Moby and Tim standing in the mountains. Moby opens a can of soda and the fizz sprays out. TIM: Um, yeah, that's what happens with gas bubbles trapped in liquid. Anyway, when the magma reaches the surface, it's called lava. Layers of hardened lava build up over time into the mountain-like formations we call volcanoes. An animation shows the volcano forming and lava shooting and flowing out of it. Hardened lava builds up the surface of the volcano. MOBY: Beep. TIM: Well, the type of formation depends on what's in the magma. Less gas means less pressure, making for gentler eruptions, like Kilauea on the island of Hawaii. Streams of thin lava from these eruptions flow far before cooling, forming flat mountains with broad slopes, kind of like a warrior's shield. That's why they're called shield volcanoes. An animation shows a shield volcano and then shows it side by side with an ancient warrior's shield. TIM: Magma with a lot of gas can build up a tremendous amount of pressure. The result is an explosive eruption that can send out pyroclastic flows, super-fast avalanches of hot ash and poisonous gas. Thick lava from these stratovolcanoes doesn't flow very far, so it piles up in steep slopes. A volcano's cross section shows a stratovolcano erupting and sending out pyroclastic flows. TIM: Washington state's Mount Saint Helens is one of these. It exploded in 1980, blowing most of its peak right off. Images show Mount Saint Helens before and after the explosion. The tip disappears. TIM: And when Mount Pinatubo erupted in 1991, its ash clouds blocked out the sun's rays and lowered world temperatures for months. An animation shows Mount Pinatubo erupting, releasing dark clouds. MOBY: Beep. TIM: Well, fortunately eruptions don't just happen anywhere. Magma only forms under special conditions, usually near the margins of tectonic plates. These are massive sections of the Earth's crust and upper mantle. The plates are in constant, slow motion, pushing together, pulling apart, and sliding past each other. A world map shows the boundary lines of the tectonic plates. TIM: Mid-ocean ridges, where plates pull apart, are the most volcanically active boundaries on Earth. The map shows mid-ocean ridges in the Pacific and Atlantic Oceans. TIM: As the plates separate, pressure on the underlying mantle decreases, allowing it to melt. The liquid magma rises to fill the gap between plates, pushing them farther out. This goes on and on, continually adding material to the seafloor. An animation shows the plates separating, the mantle melting below them, and the magma rising up between them. MOBY: Beep. TIM: Right, the Pacific Ring of Fire is another huge volcanic area. Its eruptions are fueled by collisions between ocean plates and continental plates. A map shows the Pacific Ring of Fire. Red triangles indicate volcanic sites, which are mostly in coastal areas along the west coast of North and South America and the islands and coasts of Asia. TIM: The ocean plate is denser, so it gets pushed under, or subducted. Seawater leaks into the mantle, lowering its melting point and creating magma. So when the magma erupts, it's recycling some of that old ocean crust as new land on the continent. An animation shows how a subducted ocean plate affects magma and the magma pushing up and erupting through the crust of the seafloor. TIM: In fact, geologists believe that billions of years ago, the continents first grew out of the oceans from shield volcanoes fed by subduction. The animation shows how shield volcanoes were formed from subducted plates and grew from the ocean floor over the ocean's surface. TIM: That means eruptions are ultimately responsible for just about every bit of land in the world. MOBY: Beep. TIM: Well, the Hawaiian shield volcano is a little different. It's an example of hotspot volcanism, which happens far away from plate boundaries. Geologists aren't sure whether these eruptions are caused by an unusually hot region of the mantle, or an unusually weak region of crust. The map shows a hot spot in Hawaii, which is not near a plate boundary. TIM: In any case, the near-constant lava flows on Hawaii's Big Island make it the only state in the country that's growing. MOBY: Beep. TIM: Right. If you live near an active volcano, remember that eruptions can happen at any time and without much warning. So it's important for your family to be prepared, no matter how long it's been since the last eruption. You should put together disaster kits, with things like food, water, and medicine, a battery-operated radio, a flashlight, and a mask or goggles. An animation shows the items Tim lists going into a disaster kit bucket. The food is canned, and the water is in bottles. TIM: In the event of an actual eruption, follow instructions from local authorities. Moby looks down. MOBY: Beep. TIM: Don't worry, Moby. This volcano is dormant. That means it hasn't erupted for a long time. MOBY: Beep. TIM: Of course, you never know with volcanoes. MOBY: Beep. Moby offers Tim a soda from his backpack. TIM: You, on the other hand, are more predictable. Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts